Immunoglobulin, which is a glycoprotein performing an antibody function neutralizing external antigens such as viruses, bacteria, and the like, is present in the blood or the tissue fluid. Among them, immunoglobulin G has the maximum content. The immunoglobulin G present in the blood or the tissue fluid is an important material protecting body from other external materials to be currently and widely used in fields such as protein therapeutics, diagnosis, and the like.
As the immunoglobulin G becomes increasingly used, an importance of a purification technology thereof is also increased. The currently used technology for purification of the immunoglobulin G is an affinity chromatography using protein A found in Staphylococcus. The protein A has a property of binding to Fc fragment of immunoglobulin, and thereby being used in purification of the immunoglobulin G. However, the purification method using the protein A has a disadvantage in view of high cost. In addition, elution in an antibody purification process is conducted under significantly strong acidic conditions of about pH 2 to 3, such that a probability of seriously damaging an antibody is extremely high. Further, since the protein A is significantly unstable in a high-pH solution used in the production process, the times of reuse of the protein A column is decreased, and thus, the production cost of the antibody is increased.
Accordingly, the present inventors studied to develop a repebody having a general binding protein frame with a binding capacity to various proteins, and as a result thereof, selected a novel protein having a binding capacity against immunoglobulin G, by modularity which is a structural characteristic of the repebody and the total structure analysis, based on a random mutant library. In addition, they produced and selected a novel polypeptide which is a novel repebody selectively bound to the immunoglobulin G through beneficial mutation obtained by predicting protein complex structure as a basis, and confirmed that the repebody is selectively bound to the immunoglobulin G, thereby completing the present invention.